全文获取类型
收费全文 | 67207篇 |
免费 | 7380篇 |
国内免费 | 3704篇 |
专业分类
电工技术 | 5649篇 |
技术理论 | 8篇 |
综合类 | 5124篇 |
化学工业 | 9880篇 |
金属工艺 | 4115篇 |
机械仪表 | 4280篇 |
建筑科学 | 5525篇 |
矿业工程 | 2363篇 |
能源动力 | 2046篇 |
轻工业 | 4273篇 |
水利工程 | 1612篇 |
石油天然气 | 3364篇 |
武器工业 | 800篇 |
无线电 | 7969篇 |
一般工业技术 | 7482篇 |
冶金工业 | 2836篇 |
原子能技术 | 917篇 |
自动化技术 | 10048篇 |
出版年
2024年 | 371篇 |
2023年 | 1325篇 |
2022年 | 2775篇 |
2021年 | 3638篇 |
2020年 | 2741篇 |
2019年 | 2083篇 |
2018年 | 2399篇 |
2017年 | 2608篇 |
2016年 | 2383篇 |
2015年 | 3335篇 |
2014年 | 3986篇 |
2013年 | 4686篇 |
2012年 | 5243篇 |
2011年 | 5530篇 |
2010年 | 4723篇 |
2009年 | 4410篇 |
2008年 | 4260篇 |
2007年 | 3852篇 |
2006年 | 3619篇 |
2005年 | 2973篇 |
2004年 | 2001篇 |
2003年 | 1452篇 |
2002年 | 1317篇 |
2001年 | 1051篇 |
2000年 | 1006篇 |
1999年 | 918篇 |
1998年 | 694篇 |
1997年 | 559篇 |
1996年 | 576篇 |
1995年 | 402篇 |
1994年 | 336篇 |
1993年 | 243篇 |
1992年 | 208篇 |
1991年 | 120篇 |
1990年 | 105篇 |
1989年 | 79篇 |
1988年 | 75篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 29篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1976年 | 9篇 |
1975年 | 3篇 |
1959年 | 9篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A Ml (NiCoMnA1)5 hydrogen storage alloys was prepared by double-roller rapid quenching.Its microstructure, electrochemically and kinetic characteristic were studied.A uniform crystal phase with CaCu5 structure could be detected by XRD analyses, whose average grain size is 30 ~ 50 nm and the ratio of c/a of nano-crystal hydrogen storage alloy is larger.The hydrogen absorption/desertion p - C isotherms of alloy show that its fiat-performance is perfect and the magnetic stagnant effect is very little.An simulate cell is used for electrochemical measurement.Electrode is 10C, the capacity decreasing rate via the 450 cycles at 7C is less than 20%. 相似文献
102.
Summary Well-defined water-soluble poly(styrenesulfonate)-b-poly(ethylene glycol)-b- poly(styrenesulfonate) (PSS-b-PEG-b-PSS) triblock
copolymers with narrow molecular weight distribution (1.29 < Mw/Mn < 1.36) were synthesized in aqueous solution at 70 oC via reversible addition-fragmentation chain transfer (RAFT) polymerization. The complex formed by the PSS-b-PEG-b-PSS triblock
copolymer coordinated with aluminum ion was investigated with turbidimetry, dynamic light scattering (DSL), zeta-potential,
and transmission electron microscopy (TEM). The aggregation formation was based on the neutralization of the SO3- groups in the PSS blocks with Al3+ ions. The appearance, size and stability of the PSS-b-PEG-b-PSS/Al3+ aggregates were controlled by varying the PSS block length and degree of neutralization (DN). At DN = 0.33, where the PSS-b-PEG-b-PSS
copolymer was completely neutralized with Al3+, the aggregate size increased with increasing PSS block length. The transition from the shrinking coil of small size to the
interchain aggregates of large size was found at DN of about 0.33. 相似文献
103.
固体超强酸S_2O_8~(2-)/SnO_2-SiO_2催化合成环己酮1,2-丙二醇缩酮 总被引:3,自引:0,他引:3
采用沉淀-浸渍法制备了固体超强酸S2O28-/SnO2-SiO2,以它为催化剂催化环己酮和1,2-丙二醇合成了环己酮1,2-丙二醇缩酮;考察了带水剂种类及用量、酮醇摩尔比、催化剂用量、反应时间对产品收率的影响,并用正交实验对反应条件进行了优化。实验结果表明,适宜的反应条件为:n(环己酮)∶n(1,2-丙二醇)=1∶1.6、催化剂用量为反应物料总质量的2.0%、带水剂环己烷用量5.0mL、反应时间50min。在此条件下,环己酮1,2-丙二醇缩酮收率达到91.47%;催化剂的稳定性良好,在重复使用5次后环己酮1,2-丙二醇缩酮收率为82.20%,活性下降的主要原因为催化剂表面积碳和吸附了有机物;经傅里叶变换红外光谱和气相色谱质谱分析表明,产物为环己酮1,2-丙二醇缩酮,纯度为100%。 相似文献
104.
105.
106.
Cooking reduces odor intensity in boar meat but also may induce lipid oxidation unless the meat pH is above approximately 6.0. This research was designed to determine the feasibility of cooking boar meat in the prerigor state to overcome boar odor and lipid oxidation problems. Prerigor and postrigor triceps brachii muscle samples from 40 boars (20 Duroc and 20 Yorkshire) were cooked to 60 degrees C, frozen and stored at -20 degrees C, reheated in a 60 degrees C water bath for 1 h, and then subjected to pH, thiobarbituric acid (TBA), and sensory analyses. Boar odor intensity and skatole concentration in backfat samples were determined by olfactory test and HPLC, respectively. Cooked (initial cooking) prerigor meat was found to have higher (P < .05) pH and lower (P < .05) TBA values than comparable postrigor meat (6.44 vs 6.09 and 2.15 vs 3.23, respectively). Regression analysis indicated an inverse relationship between pH and TBA values (r = -.52; P < .01). No appreciable changes in TBA values were noted after frozen storage for 14 to 98 d, but reheating increased TBA values (P < .05) in both prerigor and postrigor samples (3.45 vs 4.32, respectively). Sensory evaluation scores indicated that prerigor cooked meat was less tender with more pronounced rancid flavor than postrigor cooked meat (P < .05), but panelists may have allowed the toughness of the prerigor samples to adversely affect their flavor scores. No difference in boar odor was detected between rigor states or breeds. Mean skatole concentration in backfat was .12 micrograms/g and no difference was detected between breeds.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
107.
6-Chloro n-butyl phthalide (CBP) was orally administered to healthy, male Wistar rats pretreated with or without 3-methylcholanthrene (3-MC) by a single dose of 150 mg/kg, and urine samples were collected for 0-24 h. The urine sample was hydrolyzed with beta-glucuronidase, extracted and concentrated for TMS derivatization, and analysed on a GC-MS system for identification of CBP metabolities. Mass spectral analysis suggests that 7 CBP metabolites were present in the urine sample, and similar metabolism patterns were viewed in rats with or without pretreatment with 3-MC. Four main metabolites of CBP in rat urine were identified as alpha-beta oxolate, beta-gamma oxolate, beta-hydroxylate and gamma-hydroxylate, based on their chromatographic and mass spectral properties. Two hydroxylates have been previously identified in CBP metabolism by rat liver microsomes. The other two metabolites with higher polarity were tentatively identified as dihydroxylation products on the n-butyl side chain by the mass spectra of their TMS derivatives. One minor metabolite was found by the isotopic effect of chlorine, but its specific structure was undetermined. The difference between in vivo and in vitro metabolic profiles of CBP is also discussed. 相似文献
108.
天然调味料──酵母抽提物的研究进展 总被引:13,自引:2,他引:11
着重论述了酵母抽提物的特性、在食品中的应用前景、制造方法、工业化生产中存在的问题及其解决方法,并对酵母抽提物的发展方向作一展望。 相似文献
109.
被Kerr介质包围的J—C模型中光场位相特性 总被引:2,自引:0,他引:2
本文应用Pegg-Barnett位相理论讨论了被Kerr介质包围的J-C模型中光场的位相性质。 相似文献
110.
ElectronmicroscopicobservationsandDNAchainfragmentationstudiesonapoptosisinbonetumorcelsinducedby153SmEDTMPZhuShouPeng,Xia... 相似文献